In connection with conveyance of articles in semiconductor plants or the like, facilities such as inspection devices must process a large number wafers or the like per a unit time (these facilities have a high throughput). Accordingly, compared to the other facilities, these facilities must enhance their conveying capabilities locally, for example, around inspection devices. To locally enhance the conveying capability, it is preferable to provide random-access buffers. In an easily conceivable example, a circulating conveyor is connected to load ports of the inspection devices so that articles can be freely transferred between a carriage and a plurality of positions on the conveyor. However, to precisely transfer articles to and from the carriage, such a conveyor must be able to convey articles while maintaining a relatively high positional precision. Further, the conveyor must operate precisely in accordance with a procedure of transfer of articles to and from the carriage and with the conveyance of articles to and from the load ports. The circulating conveyor having such a precision and reliability requires large-scale facilities and a reliable system that controls the conveyor.
The Japanese Patent No. 3067656 describes that a buffer is provided between processing devices below a conveying path for an overhead vehicle. Such a buffer improves conveyance efficiency but is insufficient for facilities with a very high throughput.
It is a basic object of the present invention to easily and locally improve the conveying capability of desired facilities.
It is an additional object of an aspect of the present invention set forth in Claim 2 to efficiently utilize space and to further improve the conveyance capability of a first carriage.
It is an additional object of an aspect of the present invention set forth in Claim 3 to construct the first carriage and a second carriage using carriages of basically the same type, thus simplifying the configuration of the system and facilitating the transfer of articles between a buffer and facilities.